This invention relates to a method for converting an oxygenate feedstock to an olefin product. In particular, this invention relates to a method for converting an oxygenate feedstock to an olefin product by contacting the feedstock with a silicoaluminophosphate catalyst at an average catalyst feedstock exposure index of at least 1.0.
Olefins, particularly ethylene and propylene, have been traditionally produced from petroleum feedstocks by either catalytic or steam cracking. Promising alternative feedstocks for making ethylene and propylene are oxygenates. Particularly promising oxygenate feedstocks are alcohols, such as methanol and ethanol, dimethyl ether, methyl ethyl ether, diethyl ether, dimethyl carbonate, and methyl formate. Many of these oxygenates can be produced by fermentation, or from synthesis gas derived from natural gas, petroleum liquids, coke materials, including coal, recycled plastics, municipal wastes, or any appropriate organic material. Because of the wide variety of sources, alcohol, alcohol derivatives, and other oxygenates have promise as an economical, non-petroleum source for ethylene and propylene production.
In converting oxygenates to ethylene and propylene products, by-products are also formed. Representative by-products include alkanes (methane, ethane, propane, and larger), aromatic compounds, carbon oxides and carbonaceous deposits on and within the catalyst materials (also referred to as xe2x80x9ccokexe2x80x9d).
During conversion of oxygenates to ethylene and propylenes, coke deposits accumulate on and/or within the catalyst. As the amount of these coke deposits increases, the catalyst begins to lose activity and, consequently, less of the feedstock is converted to the ethylene and propylene products. At some point, the build up of these coke deposits causes the catalyst to reduce its capability to convert the oxygenates to ethylene and propylenes, and the catalyst is considered deactivated. Once a catalyst becomes deactivated, it must be removed from the reaction vessel and replaced with activated catalyst. To reduce catalyst costs, activated catalyst is obtained by removing the coke deposits from the deactivated catalyst. This process is typically referred to as regeneration, and typically takes place in a vessel called a regenerator.
Catalyst regeneration is typically accomplished by removing the deactivated catalyst from the reactor vessel, burning off the coke material in the regenerator to re-activate or regenerate the catalyst, and returning the regenerated catalyst to the reactor. Conventionally, the regenerated catalyst is returned to the reactor via an inlet near the bottom quarter of the reactor. By returning the regenerated catalyst near the inlet of the reactor, the regenerated catalyst can immediately contact feed and begin the conversion reaction.
Regeneration processes have been previously described in the literature. For example, U.S. Pat. No. 4,873,390 to Lewis et al. teaches a process for catalytically converting a feedstock into a product in which the feedstock is contacted with a partially regenerated catalyst. Lewis et al. describe that a partially regenerated catalyst improves the selectivity of the process to ethylene and propylene products.
U.S. Pat. No. 5,157,181 to Stine et al. discloses the use of a moving bed reactor. Catalyst is added to the reactor in a manner that is considered to be effective in enhancing conversion of feed to the desired product without enhancing conversion to by-product. This is accomplished in a preferred embodiment using a radial flow reactor design. Catalyst flows through an annulus in the reactor, with feed contacting the catalyst in a direction transverse to catalyst flow. The patent teaches that production of propane by-product decreases as the catalyst becomes deactivated. In accordance with this finding, it is generally suggested that regenerated catalyst that is recycled to the reactor should be added at an effective rate to provide sufficient active sites to enhance the production of ethylene and propylene without enhancing the production to propane.
Bos et al., Ind. Eng. Chem. Res., 1995, 34, 3808-3806, disclose computer evaluations of commercial-scale reactor types that can be used in methanol-to-olefins processes. It was found that under certain conditions partially regenerated catalyst was more desirable for ethylene selectivity compared to a fully regenerated catalyst. It was uncertain, however, whether partially coked catalyst from a reactor was comparable to a partially decoked catalyst from a regenerator.
In converting oxygenate-containing feedstock to ethylene and propylene product, better selectivity to olefin product, as well as away from undesirable by-product, is still needed. It is particularly desirable to obtain product high in ethylene and/or propylene content, while reducing the amount of any one or more of the C1-C4 paraffin by-products.
This invention provides various embodiments in an improved making of making olefin product from an oxygenate feedstock. In one embodiment, the method comprises providing a silicoaluminophosphate (SAPO) molecular sieve catalyst; and contacting the catalyst with the oxygenate-containing feedstock in a fluidized bed reactor system with continual regeneration at an average catalyst feedstock exposure (ACFE) index of at least 1.0. As defined herein, the ACFE index is the total weight of oxygenate plus hydrocarbon fed to the reactor divided by the total weight of fresh and regenerated SAPO molecular sieve (i.e., excluding binder, inerts, etc., of the catalyst composition) sent to the reactor, both total weights measured over the same period of time. Fresh catalyst, as used herein, is catalyst that has not been previously used in a reaction process.
In another embodiment, the method comprises contacting the oxygenate-containing feedstock with a silicoaluminophosphate molecular sieve catalyst in a fluidized bed reactor system with continual regeneration under conditions effective to convert the feedstock to an olefin product; separating the olefin product from the catalyst; regenerating a portion of the separated catalyst; and contacting the regenerated catalyst with additional oxygenate-containing feedstock at an ACFE index of at least 1.0.
In yet another embodiment, the method comprises contacting the oxygenate-containing feedstock with a silicoaluminophosphate molecular sieve catalyst in a fluidized bed reactor system with continual regeneration under conditions effective to convert the feedstock to an olefin product; separating the olefin product from the catalyst, and separating the catalyst into a first catalyst portion and a second catalyst portion; regenerating the first catalyst portion under conditions effective to obtain a regenerated catalyst having a coke content of less than 2 wt. %; and combining the regenerated catalyst with the second catalyst portion and additional oxygenate-containing feedstock at an average catalyst feedstock exposure index of at least 1.0.
In another embodiment, the method comprises contacting the oxygenate-containing feedstock with a silicoaluminophosphate molecular sieve catalyst in a fluidized bed reactor system with continual regeneration under conditions effective to convert the feedstock to an olefin product; separating the olefin product from the catalyst, and separating the catalyst into a first catalyst portion and a second catalyst portion; regenerating the first catalyst portion under conditions effective to obtain a regenerated catalyst having a coke content of less than 2 wt. %; contacting the regenerated catalyst with the separated olefin under conditions effective to produce additional olefin product and to obtain a selectivated catalyst; and combining the selectivated catalyst with the second catalyst portion and additional oxygenate-containing feedstock under conditions effective to convert the additional oxygenate-containing feedstock to olefin product.
In still another embodiment, the method comprises providing a silicoaluminophosphate molecular sieve catalyst; and contacting the catalyst with the oxygenate-containing feedstock in a fluidized bed reactor system with continual regeneration at an average catalyst feedstock exposure index of at least 1.0, an average gas superficial velocity of greater than 1 meter per second, preferably greater than 2 meters per second, and under conditions effective to convert the oxygenate-containing feedstock to olefin product.
In still another embodiment, the method comprises providing a silicoaluminophosphate molecular sieve catalyst; contacting the catalyst with an oxygenate-containing feedstock in a fluidized bed reactor with continual regeneration at an average catalyst feedstock exposure (ACFE) index of at least 1.5, and under conditions effective to convert the oxygenate-containing feedstock to olefin product which contains a ratio of wt. % of propylene to wt. % of propane of at least 20.
In yet another embodiment, the method comprises providing a silicoaluminophosphate molecular sieve catalyst; contacting the catalyst with an oxygenate-containing feedstock in a fluidized bed reactor system with continual regeneration at an average catalyst feedstock exposure (ACFE) index of at least 1.5, including temperature and pressure conditions effective to convert the oxygenate-containing feedstock to olefin product; and separating the olefin product into at least two olefin fractions, with one of the fractions containing at least 95% propylene and at least 90% of the propane contained in the olefin product.
In the embodiments, the oxygenate-containing feedstock preferably comprises at least one compound selected from the group consisting of methanol; ethanol; n-propanol; isopropanol; C4-C20 alcohols; methyl ethyl ether; dimethyl ether; diethyl ether; di-isopropyl ether; formaldehyde; dimethyl carbonate; dimethyl ketone; acetic acid; and mixtures thereof The silicoaluminophosphate catalyst is preferably comprised of a silicoaluminophosphate molecular sieve and a binder.
In a preferred embodiment, the silicoaluminophosphate molecular sieve is selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, metal substituted forms thereof, and mixtures thereof
The silicoaluminophosphate molecular sieve has a Si/Al2 ratio of less than 0.65, preferably less than 0.4, in yet another preferred embodiment. In another preferred embodiment, the oxygenate-containing feedstock is contacted with the silicoaluminophosphate catalyst at 200-700xc2x0 C., preferably at 400-600xc2x0 C.
In another preferred embodiment, the oxygenate-containing feed stock is contacted with the silicoaluminophosphate catalyst in a reactor at an average gas superficial velocity of greater than 1 meter per second, preferably greater than 2 meters per second. It is also preferred in certain embodiments that the silicoaluminophosphate catalyst contacting the oxygenate feedstock contains an average level of 1.5-30 wt. % coke material.